Hitherto, a PVA film has been used, utilizing its water solubility, in applications for packaging (unit packaging) of chemicals such as an agricultural chemical and a detergent, a film for (water pressure) transfer printing, sanitary goods such as a napkin and a paper diaper, a filth-treating good such as an ostomy bag, a medical supply such as a blood-adsorbing sheet, temporary substrates such as a raising seedling sheet, a seed tape and a foundation cloth for embroidery, and the like.
In particular, in the application for unit packaging of chemicals such as an agricultural chemical and a detergent, there are advantages that time for weighing a chemical for each occasion of use can be saved and there is no occurrence of getting hands dirty.
As a water-soluble unit packaging bag for use in such applications, there are known, for instance, a water-soluble film comprising a modified polyvinyl alcohol containing 1 to 10% by mol of carboxyl group and having a degree of saponification of 80% by mol or more and a viscosity of 46 cps or more at 20° C. of 4% by weight aqueous solution thereof (see e.g., Patent Document 1); a water-soluble film comprising a modified PVA having a modification ratio of an anionic group of 2.0 to 40.0% by mol and a water-insoluble or sparingly-soluble fine powder having an average particle size of not more than 150 μm (see e.g., Patent Document 2); a water-soluble film incorporated with 5 to 30 parts by weight of a plasticizer, 1 to 10 parts by weight of a starch, and 0.01 to 2 parts by weight of a surfactant, based on 100 parts by weight of PVA (see e.g., Patent Document 3); a water-soluble film incorporated with 0.1 to 20 parts by weight of a reducing agent based on 100 parts by weight of a PVA resin (see e.g., Patent Document 4), and the like.
However, in such known water-soluble films, there arise problems that the color of the films is gradually changed into pale yellow by heat history received at the time of film formation and contact with a chemical to be packed and thus the commercial value of the products is remarkably impaired, and the like.    Patent Document 1: JP-A-4-170405    Patent Document 2: JP-A-10-060207    Patent Document 3: JP-A-2001-329130    Patent Document 4: JP-A-9-316270